At 4 years of age former 23 weekers have a 36% chance of having normal neurodevelopmental outcomes, 13% have mildly abnormal outcomes and 51% have severely abnormal outcomes (n=53)

I would refer you to an article entititled Survival and Long Term Neurodevelopmental Outcomes of Extrememly Premature infant Born at 23-26 weeks Gestational Age at a Tertiary Center by Ronald Hoekstra, Bruce Ferrrara, Robert Couser, Nathaniel Payne, and John Connett, The article appeared in Pediatrics Vol 113 January 2004